Process for centrifugal separation



Patented Aug. 21, 1934 PROCESS FOR CENTRIFUGAL SEPARATION Julien Berg, Tirlemont, Belgium, assignor to Raffinerie Tirlemontoise Socit Anonyme, Tirlemont, Belgium, a corporation Application May 20, 1930, Serial No. 453,886

Germany March 5, 1927 Claims. (01. 127-56) 4 This invention pertains to the general class of processes for the separation of liquids from solids, and particularly to the class of processes for the centrifugal separation thereof. The invention 5 pertains more particularly to the regulation or prevention of the circulation of air through the mass during the rotation of the basket of the centrifuge, thus preventing a substantial degree of solidification of the liquid matter by evaporation.

The invention will be described in connection with the manufacture of sugar. However, it is understood that it may be applied to the manufacture of many other products.

In the manufacture of sugar, sugar crystals are produced by crystallization from solution and are thus obtained, coated with various quantities of adhering syrup or mother liquor. This syrup or mother liquor is generally separated from the sugar crystals in centrifuges which are more or less specially adapted for this purpose.

The centrifuges employed prior to my invention;

however, permit the circulation of air through the mass. This results in a certain degree of drying of the syrup or mother liquor, and causes the same to become more viscous and to adhere more tenaciously to the surfaces of the sugar crystals. In some instances the syrup or mother liquor may be dried to such an extent as to form a hard lacquer-like coating around the individual 3') crystals or groups of crystals.

Prior to my invention disclosed in my copending application Serial Number 167,578, filed February 11, 1927, which has resulted in Patent 1,775,385, dated Sept. 9, 1930, it was impossible to completely separate sugar solutions, such as syrup or mother liquor, from sugar crys ls without washing the crystals in the centri fl ge. The washing was accomplished by introducing a washing fluid, such as water, steam or syrup, into the centrifuge while in operation. The above mentioned drying of the sugar solution with the attendent increase in its adherence to the sugar crystals made necessary the use of larger quantities of washing fluids. The use of washing fluids greater centrifugal forces are required to drive the sugar solution from the surfaces of the sugar crystals. While, by using centrifugal forces above 800 times the weight of the mass in the centrifuge and up to the amount requiredwhich may co be as high as 7,000 times the weight of the mass or more as disclosed in my copending application,

I am able to separate adhering sugar solutions from sugar crystals even though the sugar solution be in a pasty state, it is of course obvious that somewhat greater centrifugal forces are required due to the increased adherence of the sugar solution when in a more viscous condition. It is, of course, understood that a certain loss of power results from the necessity of using the relatively higher high centrifugal forces.

Prior to the invention set forth in my copending application, the art was unable to completely discharge the adhering sugar solutions from the sugar crystals without washing mediums. However, by the use of the invention set forth herein in prior art centrifuging an increase in the degree of such separation without washing may be effected due to the absence of drying.

There are various types of apparatus by means of which my invention may becarried into practice. A few examples are shown more or less diagrammatically in the drawings. However, it is understood that this is merely by way of illustration, and that the invention is not limited thereto. In the drawings,

Figure 1 is a sectional elevation of a portion of a centrifuge, part of which is shown in broken lines, illustrating one form of apparatus capable of carrying out the invention. 90

Figure 2 is a sectional elevation through a portion of a centrifuge, part of which is shown-in broken lines, illustrating another form.

Figure 3 is a view similar to Figure 2 but illustrating a third form.

Figure 4 is a sectional elevation through a centrifuge, part of which is shown in broken lines, illustrating a fourth form.

Figure 5 is a view similar to Figure 2, illustrating the liquid air-seal resulting from the op- 100 eration of the particular structure shown.

Figure 6 is a view similar to Figure 3, illustrating another form of liquid air-seal.

Figure 7 is a sectional elevation through a centrifuge, part of which is shown in broken lines 105 and illustrating another form.

Figure 8 is a sectional elevation, part of which is shown in broken lines, illustrating a somewhat different form.

Figure 9 is a sectional elevation, part of which 110 isshown in broken lines, illustrating a differentform of trap.

Figure 10 is a sectional elevation, part of which is shown in broken lines, illustrating a labyrinth trap. Referring to the drawings, at 10 is shown a conventional basket enclosed by a casing 11.

The basket 10 is mounted upon a shaft shown conventionally at 12 and by means of which rotary movement is imparted to the basket. It

exhausting air from the casing enclosing thef basket.

In the form shown in Figure 1, the casing 11 completely encloses the basket 10 except for the opening shown at 13. The casing 11 is otherwise fitted about the moving'parts so. as to form an air-tight enclosure about the basket 10. To form a vacuum or a partial vacuum in the casing 11 fan blades 14 are caused to revolve in the opening 13. The. fan blades 14 may be of any desired number, and are so arranged that when in motion their action tends to exhaust air from within the casing 11.

One means of mounting the fan blades 14 is shown in Figure 1 wherein the shaft 12 is provided with an extension 15-upon which the fan blades are mounted as shown at 16. However, it is understood that any other form of mecha-'- nism for the operation of the fan blades may be provided.

11, making same'air-tight, and -.then build up a vacuum within the casing 11-of asuflicient value to prevent circulation or to regulate the same.

Any suitable exhausting device may be used for this purpose.

Another means for. decreasing or preventing the circulation of air through-the basket is to provide means adjacentthe outer wall of the basket which will permit the flow of a liquid but which will not permit-the flow of a gas. Suitable devices for this purpose are shown in Figures 2, 3, 5, 6, 9 and 10.

In Figure 2, for instance, the outer wall 1'7 .is. provided with a plurality of pocket forming channels 18. The channels 18 are shown more or less 8 shaped. However, it is understood that the channels 18 may be of any convenient shape so as to form a pocket within which the liquid will collect in sufficient amount to close the channelwhen the device is' in operation. The seal thus provided will not permit the flow of gases but will permit the flow of liquids. The thickness of the wall of liquidin the pocket is increased by liquid entering the channel 18. An increase inthe thickness of the wall of liquid results in a part of the liquid being forced into portion 21 of the i channel 18 from which it is discharged to theexterior. .The total centrifugal force applied to .20 is'always covered by the inner surface 24 of. the liquid held in the pocket 22. 1

.tions 25 and 26 which tip is at all times covered the'basket.

in a radial direction than the wall of liquid acting upon the portion 19. The result is that a portion of the liquid in the reversing portion 20 is forced into the outlet portion 21 of the channel 18.

The area covered by'the pocket is clearly illustrated in Figure 5 wherein the darkened portion in pocket 22 represents the minimum amount of liquid which remains in the channel 18 while.

the centrifuge is in motion. The condition represented in Figure 5 exists when all of the liquid has been discharged from the basket, but the basket is still in motion. An efiective seal is provided at all times inasmuch as the tip 23 formed at the intersection of the portions 19and The portion 20 is shown having a downward slope in order that the liquid will drain from the pocket to the outside of the basket when the basket is stopped. However, the portion 20 may be horizontal or inclined if this may be desired for any reason.

The channels 18 need not have three portions such as shown in Figures 2 and 5 but may be made up of two portions as shown in Figures 3 and 6. In this case there isan inlet portion25 and an outlet portion 26 so as to form a pocket 27 illustratedby the darkened portion in Figure 6. In this case a tip 28 is formed by the intersecting porby the fluid held inithe pocket 27 while the basket is in motion. By means of this construction the liquid may be made to escapefrom the bottom of Other forms of channels will suggest themselves to persons skilled in theart and familiar with this invention. For instance, a tube having its outer end U-shaped or I-shaped or otherwise, to provide a reversing'channel, might be substituted for either of the forms shown in Figures 2, 3, 5 and 6. The plain ends of the tubes would be inserted into the openings 31, as shown, for instance, in Figure 4. In this case the cover 35 would be omitted. Each of the openings 31 would be provided with one of these tubes or a circumferential row at the bottom would be so provided and the remainder of the openings closed. However,'any other arrangement might be employed, In the case of a tube having a U-shaped end with the U pointing downward, all of the liquid would drain from the tube when the basket comes to rest. In

the case of a tube having an eye at its end with the opening above the lowest part of the bend, a portion of the liquid would always remain in the tube to form a seal. The outer ends of such tubes may have many other forms. For instance, the end of a tube might be straight and empty into the mouth of a cup-shaped device, the mouth of the cup being in a more or less vertical plane. Other forms of tubes will suggest themselves to I persons skilled in the art and familiar with this invention.

Centrifugals of the ordinary type can be readily adapted for app'licants purpose by merely mounting the tubes in the apertures. This can be readily effected, for instance, withscrew threads.

In the forms shown in Figures 1 and 4 the screen is formed in the outer wall 30 of the basket 10 by providing a plurality of apertures 31in the outer wall 30. In Figures 2, 3, 5 and San inner screen 32 spaced from the outer wall 1'7 is shown. The construction of such inner screens and the means of attaching same inside of the basket is known in the art and forms no part of this invention. When the screen 32 is used the solids are held within the screen and only liquids find their way into the space 33 between the screen 32 and the outer wall 17. By providing the screen 32 the channels 18 may not only be larger in diameter but may befewer in number.

about the wall of the basket. In many instances one circumferential row at the bottom of the basket would be sufficient.

Any means may be employed for forming the channels in the walls, such as drilling, casting, etc. In the form shown in Figures 2 and 5, for instance, the portions 19 and 21 may be readily drilled. The portion 20 may also be formed by drilling into the outer wall 17 at an angle so as to connect the portions 19 and 21. Sections of the portion 20 not to be used may then be plugged by any convenient means. I place by brazing, special cements, screw-threads, etc. A plug of this character is illustrated at 34.

Another means for decreasing or preventing the circulation of air through the basketis to provide the basket with a tight fitting cover 35 as shown in Figure 4. The cover 35 tightly closes the opening 36 in the basket 10, and may be secured in place by any suitable means such as clamps 37 secured in place by wing nuts 38. It is, of course, obvious that any other structure may be provided for holding the cover 35 in place'or for closing the opening 36.

' Another means for decreasingor preventing the circulation of the air through the basket is by inserting various devices between the outlets and the inlet of the basket. For instance, in Figure 7 the basket 10 is provided with a casing 40 which is adapted to support a member 41. cured to the member 41, by any suitable means such as themember 42fis a cover 43 for the opening 36 in the basket 10. The cover 43 may or may not contact the upper face of the basket 10 but is preferably not in contact therewith.

- This results in a small annular aperture 44 between the basket and the cover 43.

In operation the motion of the basket tends,

to cause the air to be thrown outward through the apertures 31 in the outer wall 30. If the opening 36 is not closed, this air returns to the basket through this opening. With the cover 43 in place as shown in Figure 7, the path of the air is completely out off. except for the aperture it and the stationary cover 43. Such vanes may,

of course, be provided if desired.

In Figure 8 annular rings 45 and 46 are secured to the inner wall of the casing 147. An annular disc-like ring 47 secured to the basket 148 is positioned between the rings 45 and 46 and may or may not be contactedthereby. In this form the rings are preferably constructed so that moving parts do not contact the stationary parts,

so that the device may operate without friction. However, the parts may operate. in contact with each other and packing may be provided if desired. A second moving. annular ring 48 shown secured to the ring 47 through an ofi-set portion 149 so as to inclose the ring '46 between It is under-- stood that the channels '18 are suitably distributed of cooperating parts may be provided between the casing and the basket. 1

The plugs may be held in the rings 47 and 48. In operation air is restricted from passing the rings due to the/churning pressure and/or other action between the rings. The ring 48 may be omitted if desired.

A second seal is shown at the bottom of Figure 8 30 which comprises an annular disc-like ring 49 secured to the casing 147 and a U-shaped annular member 50 secured to the basket 148 and inclosing the member 49. The member 49 is shown with a slight upward slope and preferably does not contact the U-shaped member 50. The liquid is conducted from the chamber 51 around the outer edgeof the basket 148 ,to the chamber 52 below the basket by means of tubes 53. Any other form Another means for carrying out the invention is shown in Figuresv 9 and 10 wherein a liquid air seal is "provided which operates irrespective ofthe movement of the basket.

In Figure 9, for instance, a cup-like member 55 is secured to the inner wall of the casing 56 and an annular member 57 having downwardly turned flange 58 dipping into the cup 55 is secured to the upper edge of the basket 59.

In operation the cup 55 is filled with liquid into which the flange 58 dips. After the cup 55 has been once filled, a refilling is unnecessary. The upper edge of the cup 55 is turned inward to retain liquid thrown against the .outer wall of the cup by centrifugal force. I

A liquid seal is also shown at the bottom edge of the basket 59 and comprises an annular'cuplike member 60 attached to the inner wallof the casing 56 and an annular memberGl secured to the lower edge of the basket 59. The member 61 has a flange-62 which/dips into the cup 60. The cup 60 is so shaped as to-leave a space 63 between the upper edge of the cup and the basket 59 to permit the liquid thrown off from the basket to flow downward into the cup 60. This structure permits the liquid to flow from the chamber 64 on the outside of the basket 59 to the chamber 65 below the basket 59. After the cup 60 is full any excess liquid flows over the inner upturned edge inner wall of the casing 69. The basket 70is 136" provided with an outer wall 71 which is imperforate. At the bottom this wall is turned outward as shown at 72 and then downward as shown at 73. Secured to the bottom of basket 70 is an annular disc-like member 74 having a down wardly extending portion 75 which dips into the cup 68. The upper edge 76 of the cup 68 is shown turned inwardly toward the casing 71 to retain liquid thrown outward by centrifugal force, but may be spaced therefrom if desired, as shown at 77. A basket of this type is provided with an inner screen 78.

In operation the liquid is thrpwn into the chamber 79 on the outside of the screen 78 and AfiOWS downward and is thrown outward between the portion-72 and-the annular member 74. It then is guided into the cup 68 by the flange 73, the liquid impinging against the outer inside wall of the cup. The excess flows over the inner upturned edge 80 of the cup 68 and falls into the chamber 81 at the bottom of the basket from which it may be removed.

Any of the means described for carrying out the process may be adapted to any type of centrifuge, no matter how it is driven, charged or discharged or otherwise constructed. Modifications of the apparatus herein shown and/or described will suggest themselves to persons skilled in the art and familiar with this invention.

By preventing the circulation of air through the masswhile in the centrifuge, the adhering sugar solution is maintained in substantially its original condition respecting fluidity and is thus fire readily discharged from the sugar cryss. I While the invention has been described with respect to the separation of sugar solutions from sugar crystals, it is applicable to any separation of liquids from solids involving similar problems.

The invention has been described in connection with a centrifuge having a basket. It is obvious that the same may apply to any other form of centrifuge having a'receptacle of any shape or contour. Many other modifications may be made within the scope of the claims without departing from the spirit of the invention.

The term air as used in the specification and claims is intended to include any gas of whatever nature.

The term unchanging" as here used is intended to mean that the atmosphere within the centrifuge is not replaced or substantially modified by extraneous air, gas or moisture during the operation of the process. The temperature of the atmosphere within the centrifuge may, however, be modified within'limits without affecting the eificiency of the process. This application is a continuation in .part of my copending application Serial Number 256,815,

by preventing the drying and consequent increase in the viscosity and stickiness of the mother liquor I during separation.

2. A process for preventing the drying and consequent increase in the viscosity and stickiness of mother liquor during the separation of adhering mother liquor from sugar crystals which comprises centrifuging a mass of said crystals and liquor in a relatively unchanging atmosphere maintained apart from the ambient air at a relatively constant volume without any substantial flow of air or other gas oven and through said mass.

3. The process for preventing the drying and consequent increase in the viscosity and stickiness of mother liquor during the separation of adhering mother liquor from sugar crystals which comprises centrifuging the mass of said crystals and liquor at a speed such that the centrifugal force developed is in'excess of about 800 times the weight of the crystals in'a relatively unchanging atmosphere maintained apart from the ambient air at a relatively constant volume without any substantial fiow of air or other gas over, and through said mass.

4. A processfor theseparation of adhering mother liquor from sugar crystals which comprises centrifuging a mass of said crystals and said liquor at a speed such that the centrifugal force developed is in excess of about 800 times the weight of the crystals in a relatively unchanging atmosphere maintained apart from the ambient air at a relatively constant volume without any substantial flow of air or other gas 'over and through'sa'id mass and without the addition of moisture, thereby preventing the drying. and consequent-increase in the viscosity and sticki-' ness of the mother liquor during separation.

5, A process for preventing the drying and consequent increase in the viscosity and stickiness of mother liquor during the separation of adhering mother liquor from sugar crystals which comprises centrifuging a mass of said crystals and liquor in a relatively unchanging atmosphere maintained apart from the ambient air at a relatively constant volume without any substantial flow of air or other gas over'and through the mass, and substantially continuously withdraw-- ing separated mother liquor from the centrifuging zone.

JULIEN BERGE. 

